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Title: A tale of two supernovae ... and an old curious star
Author: Hendry, Margaret Alice
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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Understanding the evolution of massive stars and their deaths in core-collapse supernovae is of fundamental importance not only to stellar astrophysics, but has implications for other broader areas of astronomy. Massive stars are thought to be the main drivers of the chemical and dynamical evolution of galaxies through their strong stellar winds and their explosive deaths. Supernovae are principally separated into two categories, those without hydrogen (Type I) and those with (Type II). The plateau subclass of Type II supernovae (SNe II-P) are thought to arise from the explosions of red supergiants (RSGs), which have initial masses greater than 8-10 M° and have retained their hydrogen envelopes before core collapse. Until the discovery of the 8 M° red supergiant (RSG) that exploded as SN 2003gd, there had been no direct confirmation that SNe II-P did indeed arise from the explosion of RSGs. Before this detection there had been only two other unambiguous detections of Type II progenitors, neither of which fitted the evolutionary scenario that is commonly accepted. These were the progenitors of the peculiar Type II SN 1987A (Sk —69°202), which was a blue supergiant (BSG), and the Type IIb SN 1993J that arose in a massive interacting binary system. There is at the moment only a handful of well studied and documented SNe II-P. The best observed supernova of this class to date is SN 1999em, which was followed for over 600 days at many different wavelength ranges. Because of the questions that still surround the progenitors of supernovae, it is of vital importance to understand the nature of the supernovae themselves as well as to compare them with the observed progenitor masses. This thesis tells the tales of two SNe II-P, 2003gd and 2004A, which have unambiguous detections of their progenitors with masses of 8 and 9M°, respectively. SN 2003gd is of particular importance because of the question of its nature. It was found to have a lower tail luminosity than is normal for SNe II-P, indicative of a lower ejected nickel mass. However, the supernova does not belong to the proposed group of low-luminosity supernovae, which could either be the result of the low-energy explosion of massive or low-mass stars. In the high-mass model the collapsing core forms a black hole and a significant amount of fallback of material occurs, giving the low-luminosity and low-nickel mass. Instead, SN 2003gd appears to be a member of a continuous heterogeneous group of SNe II-P. This thesis also includes a study of Sher 25, a curious BSG in NGC 3603, which has an impressive emission line nebula in the form of an apparent circumstellar ring and bipolar nebulae. The appearance of the nebula of Sher 25 bears a striking similarity to the rings around the remnant of SN 1987A, which were almost certainly there before the supernova exploded.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available